So-called telephonometric measurements, designed to test the performance of electroacoustic transducers such as the receivers and transmitters of telephone handsets, are advantageously carried out automatically with the aid of devices simulating human ears and mouths. This not only saves manpower but also allows the standardization of testing equipment according to internationally established specifications.
Thus, an artificial ear of the type here envisaged is a phonometric device which acts as an acoustic load for a telephone receiver and whose sensitivity/frequency characteristic should correspond as closely as possible to that of the human ear. A microphone forming part of the device translates the incoming sound waves into electrical signals which are sent to a measuring circuit for evaluation of the response characteristic of the receiver undergoing testing.
The International Electrotechnical Commissioner (IEC) has proposed an artificial ear whose adoption for telephonometric measurements was provisionally recommended by the CCITT during its 5th Plenary Assembly (see Green Book, Vol. V, recommendation P51).
The IEC artificial ear simulates the performance of a human ear whose auricle or pinna is tightly pressed against the earpiece of a telephone handset so that no acoustic leakages occur between the telephone receiver and the ear. In practice, however, a user will press the receiver tightly against his ear only under extraordinary circumstances, as where the signal is very faint or the telephone is located in a noisy room. Normally, the handset is held close to the ear but with enough clearance to generate significant acoustic leakage.
Thus, a telephone receiver tested with the IEC artificial ear and found to have a substantially frequency-independent response may not perform satisfactorily in actual use.